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Wiring center tapped transformer secondary for most power

Discussion in 'General Electronics Discussion' started by pierre1, May 1, 2011.

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  1. pierre1

    pierre1

    3
    0
    May 1, 2011
    I have a 64v CT transformer. The project is a 32v DC power supply. I want to maximize the current for the single load. All else being the same (load, ripple filter, etc) what rectifier setup would have the most power @ 32v available for the load? Let's assume the diodes aren't the limiting factor.

    1. Full bridge rectifier (4 diodes) between the center tap and one leg (wasting 1/2 the secondary)
    2. Full wave (2 diodes) one on each leg, the CT is ground

    I'm not sure this last one is possible, but...
    3. 2 Full Bridges - One between the CT and one leg, the other between CT and second leg, with the outputs in parallel. My thinking - with respect to the CT, each leg is 180deg out of phase. However after the bridge one would have the same 120hz wave.

    Ideally I would cut the center tap to separate the coils and then put them in parallel with a single bridge, but I am trying to avoid having to do that - getting it cut and unsoldered off the terminal with enough length to solder a wire on will be tricky. Would hate to try and have it not work rendering the trans useless.
     
  2. duke37

    duke37

    5,364
    770
    Jan 9, 2011
    Option 2 is the way to go, the heat in he transformer is spread in both output windings and there is only one diode voltage drop.
    If you split the winings it may not be possible to place them in parallel unless they are closely matched. Two bridge rectifiers, each being supplied by a winding will stop currents flowing the wrong way if the windings are not matched.
     
  3. pierre1

    pierre1

    3
    0
    May 1, 2011
    Won't 1 and 2 have the same power output? 1 uses the full wave from half the secondary. 2 uses the lower part of one with the upper part of the other. 3 will use the full part of both, doubling the power of 1 or 2. Or is my logic flawed?

    I don't mind the voltage drop, regulated voltage will be several volts lower.

    Thanks for your response!
     
  4. duke37

    duke37

    5,364
    770
    Jan 9, 2011
    The power output is limite by the heating of the windings. The transformer will be designed so that total heat in the primary, secondary1 and secondary2 is minimised. If you use one secondary only, the heat will be doubled in that winding so the loading should be a little lighter.

    I do not see how you wire option 3 without a short. I think the only way is to split the windings. However, remember that there is a heat dissipation limit in the primary also. a well designed transformer will have equal losses in primary and secondary so reducing secondary losses a little will not enable much increased power output.
     
  5. pierre1

    pierre1

    3
    0
    May 1, 2011
    Ok, I think I get it now. Even if I split the windings and put them in parallel with a full bridge I will still get approximately the same output power as choice 2. I may as well stick with that method then. Thanks again!
     
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